What is a Variable Frequency Drive?

What is a VFD?

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.

Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.

How does a Variable Frequency Drive work?

The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives.

Let us assume that the drive is operating on a 480V power system. The 480V rating is “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can see, the VFD dc bus has a dc voltage with an AC ripple. The voltage runs between approximately 580V and 680V.

We can get rid of the AC ripple on the DC bus by adding a capacitor. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system. This capacitor absorbs the ac ripple and delivers a smooth dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, the voltage on the DC bus becomes “approximately” 650VDC. The actual voltage will depend on the voltage level of the AC line feeding the drive, the level of voltage unbalance on the power system, the motor load, the impedance of the power system, and any reactors or harmonic filters on the drive.

The diode bridge converter that converts AC-to-DC, is sometimes just referred to as a converter. The converter that converts the dc back to ac is also a converter, but to distinguish it from the diode converter, it is usually referred to as an “inverter”. It has become common in the industry to refer to any DC-to-AC converter as an inverter.

Note that in a real VFD, the switches shown would actually be transistors.

When we close one of the top switches in the inverter, that phase of the motor is connected to the positive dc bus and the voltage on that phase becomes positive. When we close one of the bottom switches in the converter, that phase is connected to the negative dc bus and becomes negative. Thus, we can make any phase on the motor become positive or negative at will and can thus generate any frequency that we want. So, we can make any phase be positive, negative, or zero.

The blue sine-wave is shown for comparison purposes only. The drive does not generate this sine wave.

Notice that the output from the VFD is a “rectangular” wave form. VFD’s do not produce a sinusoidal output. This rectangular waveform would not be a good choice for a general purpose distribution system, but is perfectly adequate for a motor.

If we want to reduce the motor frequency to 30 Hz, then we simply switch the inverter output transistors more slowly. But, if we reduce the frequency to 30Hz, then we must also reduce the voltage to 240V in order to maintain the V/Hz ratio (see the VFD Motor Theory presentation for more on this). How are we going to reduce the voltage if the only voltage we have is 650VDC?

This is called Pulse Width Modulation or PWM. Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. While this would not be practical for plumbing systems, it works very well for VFD’s. Notice that during the first half cycle, the voltage is ON half the time and OFF half the time. Thus, the average voltage is half of 480V or 240V. By pulsing the output, we can achieve any average voltage on the output of the VFD.

See the Pictures below to understand what the different parts of a drive look like.

Why should I use a VFD?

1 - Reduce Energy Consumption and Energy Costs

If you have an application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with a variable frequency drive, which is one of the benefits of Variable Frequency Drives. VFDs allow you to match the speed of the motor-driven equipment to the load requirement. There is no other method of AC electric motor control that allows you to accomplish this.

Electric motor systems are responsible for more than 65% of the power consumption in industry today. Optimizing motor control systems by installing or upgrading to VFDs can reduce energy consumption in your facility by as much as 70%. Additionally, the utilization of VFDs improves product quality, and reduces production costs. Combining energy efficiency tax incentives, and utility rebates, returns on investment for VFD installations can be as little as 6 months.

2 - Increase Production Through Tighter Process Control

By operating your motors at the most efficient speed for your application, fewer mistakes will occur, and thus, production levels will increase, which earns your company higher revenues. On conveyors and belts you eliminate jerks on start-up allowing high through put.

3 - Extend Equipment Life and Reduce Maintenance

Your equipment will last longer and will have less downtime due to maintenance when it’s controlled by VFDs ensuring optimal motor application speed. Because of the VFDs optimal control of the motor’s frequency and voltage, the VFD will offer better protection for your motor from issues such as electro thermal overloads, phase protection, under voltage, overvoltage, etc.. When you start a load with a VFD you will not subject the motor or driven load to the “instant shock” of across the line starting, but can start smoothly, thereby eliminating belt, gear and bearing wear. It also is an excellent way to reduce and/or eliminate water hammer since we can have smooth acceleration and deceleration cycles.

Sir if my supply voltage is 400v 60hz and the supply voltage for a certain motor is 460v 60hz, could i use a vfd just to compensate the 460v requiremebt of the motor?

Yin (Admin):

26/03/2018, 03:57:32 PM

Mark,

You can try using your VFD but it will likely run into over current issue at full speed (60Hz). The proper way to fix this is to either get a transformer to boost your incoming voltage to 460V, or find a 400V motor and pair it with a VFD. Most VFDs can be run at 380-480V. Hope this helps.

Hello
I am from India. I have a VFD 90kW in my factory for controlling a compressor. Recently the line input reactor completely burnt (All the 3 phases) and also the reactor's core got welded with the panel board and the 2 input line fuses of 250 Amps blown out. We are not able to find the reason for such a huge failure. Now the condition of the VFD is if I apply input 415 VAC 3 phase, the drive switches ON and the display of the drive's operators panel is also in ON condition. I called a power electronic service person and inspected the VFD, he said the VFD is not having any shorts between the 3 phase AC input and the DC bus. Also he told there is no shorts between DC bus and 3 phase output of the VFD. Also in my VFD panel the 3 phase power line filter also got damaged.

Now I have placed order for the same type of reactor, replaced the fuses and the 3 phase power line filter. I would lie to now whether I need to check any insulation resistance between the VFD input 3 phase terminals and body of the VFD also the same for the output using megger of 500V. I tested the resistance between the 3 phase input and body of the VFD and the same for the output using a Digital multimeter (DMM), I am getting only 3 to 5 meg ohms, is that fine ?. But I have not tried anything with megger. Kindly let me know why the Reactor failed and what may the cause of failure. Kindly help me by sending me the above details, to avoid such breakdown in future.

Thank u for spending your valuable time reading my message and for replaying.

May I know if there are any Advantages if I go for a oversize VFD drive, My motor power is 1/2 HP

Yin (Admin):

21/02/2018, 11:18:41 AM

Santosh,

Going with a bigger VFD will allow you to have the flexibility to use it on bigger motors in the future, and your VFD will not be running as hot because it is not using its full capacity. Hope that helps!

Hu sir, Good evening all, we are dealing with scrubbers and waste water treatment systems. In our Scrubber system WE NEED TO CONTROL THE SUCTION FAN(CENTRIFUGAL) SPEED BY OUR 4-20 MA FROM THE MASS FLOW METER USING – VARIABLE FREQUENCY DRIVE(VFD). So please advise our queries below,

1. Is it possible to control the fan speed with our 4-20ma Mass Flow Meter signal using VFD ?
2. Can VFD have the provision to connect our 4-20 ma ?
3. What methods/Signals required, Normally to control the fan speed using VFD
4. Please Attach their detailed brochures
5. And factors to consider for selecting your VFD

Thank you and looking your Expertise advice asap please.

Drew (Admin):

10/04/2018, 10:03:07 AM

Good questions! I’ve replied in order:

1) Yes. VFDs are designed to control the speed of your electric motor in order to better suit the application you are using it for. You can program your VFD to run at different speeds for different mass flow meter(or other devices) readings.
2) Virtually all current VFD models can accept a 4-20 mA signal.
3) VFDs can use a variety of different signals, from a variety of different sources. While 4-20mA is a very commonly used, there are many others such as 0-5V, and 0-10V, just to name a few.
4) When selecting a VFD, you need to first ensure that it will accomplish what you need accomplished. Beyond that you’d be looking for one with a good cost/value ratio. Our drives are competitively priced, have great longevity and a have a variety of features to help your operation run efficiently.

Thank You very much for a nice & useful interpretation about VFD function. I am grateful to You. We the readers have more requirements as we are not pre experts & professionals in this sector. So I am expecting if it is possible to explain the function of each components of VFD by visualizing in Oscilloscope when the Motor is running (controlling the speed) (conversion of AC-DC-AC, Diode function, Capacitor function, Magnitude of AC & DC Voltage, Changing Frequency & current etc.). A 3 phase Motor is running by VFD. How I will measure the variable(instentenious) frequency as well as voltage ? As far I know, Power(P)=Torque(T) X RPM. Three situations can be happend (1) T is constant RPM is variable. (2) RPM is cons. T is variable. (3) Both are variable. How these three situations are handled by VFD ? If it is possible please explain.

Hi,
I am using a 55 kw motor and the motor is controlled by VFD. The full load current of motor is 88 A. The warning current is set at inverter as 98 A. But inverter is trippng for load current of 71 A itself and alarm message comes as "overcurrent". Can you please help?

Dear Sir,
Your blog is really informative. I am trying to understand VFD and its application on a EOT hoist. I am interested to know: "By any means , is it possible to use vfd voltage or current ratings to detect if the hoist is holding a load or not ?" .......... Any information provided by you would be helpful and shall provide me directions to learn better....

Sir,
we are using a vfd, when we increase the frequency upto 37 hz, it is working fine.if we increase above 38 hz the voltage will raise upto 670v between phase to phase & vfd trips.
what may be the problem, please suggest.

hi sir
if we adjust the VFD in 25HZ what will be the output voltage in the motor.is this formula working to calculate the voltage Vo=vt/ft*fs
where vo is out put voltage
vt is total voltage or supply voltage
ft is high frequency 50hz
fs is set point frequency. thanks.

Hi. I replaced my wood lathe motor with a Hitachi 2HP/3PH motor rated at 200V and 6A FLA at 60 Hz. I am now shopping for a proper 1PH input/3PH output VFD with the proper specs.

1. Can I independently control (while maintaining the Hz I want) the VFD 3PH output to not exceed 200V? Or is applying 220V output still safe for the motor even in the long term? As mentioned, my expected motor loads will always be light to rarely medium.

2. Considering the lathe's light duty, I was hoping that a 3HP VFD will do the job?

Question: I am working on a stock water pipeline. The well will also service some corals and a residence. A 3 hp pump will be required to run the system and pressure reducers will be placed on the coral and residential lines. The problem is that static pressure from the stock water line is about 150 psi at the well. Can a VFD handle that kind of static pressure? Thanks for your input!

We have 180hp/2900rpm/3phase motor which runs centrifugal air blower at 160amps in normal conditions but sometimes we have to run this blower at lower flow rate by throttling discharge valve, can we use VFD, if yes what should be the specifications of VFD to float purchase inquiry. Thanks

Connor (Admin):

13/06/2017, 02:10:43 PM

Virender,
Yes, this is a perfect application for a VFD. Based on the provided specifications, the FR-F840-01800-3-60 would be a good fit. If you want to double check everything give us a call at 1-800-800-2261.

My Motor full speed is 995 rpm ( 415V, 50 Hz ), Can I increase the speed to 1100 RPM?
With VFD can we increase the speed of the motor beyond the stated RPM in the motor rating plate?

Connor (Admin):

25/05/2017, 02:29:58 PM

Bhuvan,
Yes. You'd want to raise the max input Frequency to ~55.28 Hz. With VFDs you can increase the speed of the motor beyond the stated nameplate RPM value, but you do lose some torque when doing so.

Say you have a VFD with a single phase input (generating 3ph rectangular wave form at output) vs a VFD with a real 3ph input. Am I to assume the second VFD will generate a true 3ph sine wave at output, or still rectangular like in the case of 1ph input? In any case - practically speaking - would I see a difference in the way the motor is running? Smoother, quieter, less whistles and whines?

Yin (Admin):

25/04/2017, 11:33:33 AM

Tom,

No, there won't be any differences. It will generate a sine wave at output. VFDs are often used as a method of phase conversion. Sometimes it is cheaper than a phase converter (usually smaller HP/kW), sometimes it isn't. Hope that helps.

How can I install the VFD for my domestic and commercial use
R.Kumar.Hyderabad, India

Yin (Admin):

13/04/2017, 09:03:33 AM

Kumar,

Each product manuals provide installation guides. After you connect the power cables, you need to program your VFD, which is different in every brand. We strongly recommend you to hire an electrician to install this for you if you have no experience in installing VFDs.

Hey guys, I want to buy a 30 hp Nema D electric motor for a research project in my lab. The Locked Current is 213A @ 460V and full load current is 38A @ 460V. My lab power supply is 100A and 230V. The motor can also run on 230V. I have the following questions:

1. Will my motor run on the power supply in my lab?

2.What king of VFD would I need based on my motor specs and power supply?

I would really be very grateful for any advice. Thanks!

Yin (Admin):

31/03/2017, 05:19:30 PM

Reuven,

What is your motor's full load amps (FLA) at 230V?
What kind of application is your motor running?

Reuven Gomes:

01/04/2017, 03:29:06 PM

Hi Yin,

I'm not sure. Since the FLA @460V is given as 38A, @230v it should be 76A right? I'm not completely sure. The dealer I'm buying it from said the fuse chart shows 98A @ 230V for the 30 hp motor and 60A @ 230V for the 20hp. So is that the FLA?

Also, the motor is being used to drive another engine called an optical engine on which I perform tests. It is a large diesel engine, a cummins VT-903. 4 cylinders have been cut off and we inject different fuel into one of the remaining two of which one cylinder has no compression(holes made in the head) so it just helps balance the engine. So essentially, this motor has to start rotating the engine from rest and maintain a speed of 600rpm. I need a VFD to just manually control the speed. A friend of mine using a 10hp motor for an identical application except his engine is a Ford Mustang v8(whole). No compression in 7 of the 8 cylinders though. He is using a Mistsubishi D700 VFD.

Yin (Adam):

03/04/2017, 09:40:51 AM

Reuven,

Theoretically yes, if it is 38A at 460V, it should be 76A at 230V. That is the FLA. It should show on your motor nameplate also.

So the D700 only goes up to 10HP, and the E700 goes up to 20HP. For a 30HP, you will likely need to go to the F800 series. Check out this one FR-F820-00930-3-N6.

Are you making your own electric car? Is space a concern?

Reuven Gomes:

03/04/2017, 10:59:06 AM

Yin,

I have contacted the motor agent to ask what the FLA is on the nameplate.

And no, I'm not making an electric car. Like I said, it's basically coupled on another engine and rotates it since the engine cannot sustain itself on the combustion tests. The combustion we test for is too weak and just for research. So to answer your question, no, space is not an issue. I'm just going to set up on my table next to the PC.

Are there any cheaper alternatives to the Mitsubishi VFDs? My friend said that they are one the easiest to operate and that's why he bought that one but he got it much cheaper on ebay. Do you have any suggestions? I need it to be able to handle the motor and to be easy to operate. I'm not automating it. Will manually enter the speed each time. Also, it's going to be in a lab and hence not subjected to any harsh environmental conditions.

Yin (Admin):

03/04/2017, 11:11:07 AM

Ok I see. Mitsubishi is quite user friendly, and very reliable. Your friend's drive is much cheaper because it is a micro drive, and it is only 10HP. There are a couple of less expensive options we can look at. Can you send me your contact number to ytang@vfds.com and I will give you a call today?

Hello team, I was asked to carryout a little project. That will consist in simulating a VFD (0.4 kw/0.5 Hp:200-230V (input current 5.5A output 2.5A))with a 3 phase electric motor. Please i wish to know what accessories to use for such simulation. Like type of cable, relay,switch, plug etc....
Thanks.

Yin (Admin):

28/03/2017, 09:17:11 AM

Babila, I am not sure what you mean by simulating. If you want to connect a VFD, you just need 3 cables for the input, and 3 cables for the output. You can learn how to do that here: How to wire a VFD

I need to know that V/HZ ratio, so the Drive itself will automatically maintain the ratio when we set the frequency or the voltage should be also set by us.
I have some more question, will add up when you reply me.....

Yin (Admin):

21/03/2017, 12:29:35 PM

Somu, I don't understand what you are asking. Can you rephrase your question about the V/Hz ratio?

jyoti verma:

07/07/2017, 12:53:04 AM

VFD with sensor or sensorless have two control method 1) Scalar control 2) Vector control . In Scalar control we follow V/f method while in Vector Control we follow DTC ( DIRECT TORQUE CONTROL ) and FOC (FIELD CONTROL ). somu if u r using VFD might u have set parameter regarding MOTOR CONTROL MODE ( vector speed, vector torque and scalar frequency )u have to set parameter according to your appication.
For ex : i m using 1hp induction motor for filling conveyor for that i m using 1hp ABB DRIVE (MODEL ACS355) as in my application there is no load in conveyor ( filling purpose) so i m setting PARAMETER 9904 equal to 3 that is SCALAR CONTROL (V/F CONTROL)

what type of vfd could be used for drag conveyor to lower the Motor rpm but "increasing/maintaining the torque"?

(note; the said drag conv. is next from its feed screw w/ fixed rpm so lowering drag rpm/speed will increase the load to the motor,the purpose of reducing rpm is not to reduce mat'l flow but to increase mat'l bed level for efficient machine operation). the drive assembly is 3hp 440v 60hz 3ph 1780rpm motor coupled w/ 3 reduction gearbox units to achieve lower speed range,the first gb has variable speed adjuster previously where we reduce the speed but it was broken so i suggest to replace it w/ fixed rpm and install vfd to the motor.

Yin (Admin):

20/03/2017, 04:11:19 PM

Wel,

You will need a VFD that is constant torque (CT), meaning it has at least 150% overload rating. Mitsubishi makes a great constant torque VFD, and that is the A840 series. Size your VFD based on your motor amp rating, make sure the VFD has a higher maximum amperage rating.

Can we tell one vfd is in good working condition by only measuring voltage at output terminals of vfd ?

While measuring output Multimeter should be in DC mode or AC more ?

When we increase the frequency in control unit, output voltage at vfd will increase or not irrespective of motor is connected or not ?

We are using sew eurodrive.where can i get troubleshooting manual for this?

Thanks.

Jeff Condit:

08/03/2017, 04:21:00 PM

Comment No, basic VFDs do not reduce the peak voltages and so a voltmeter will not be accurate. Instead, they spread out a series of pulses alternating a group of positive ones then a group of negative ones. The overall duration of the positive and negative pulses combined is the effective period of the VFD. If you have to measure it you would be better to use an oscilloscope if you have one. Otherwise you could make a filter out of an inductor and a capacitor to help smooth out the pulses and see the overall period. Remember, the inductance and inertia of the motor smooth out the pulses coming from the VFD to make relatively smoother motion at a slower frequency that if the motor were run directly of the line.

(NOTE: It is also possible to synthesize a frequency higher than the line frequency.)

Yin (Admin):

20/03/2017, 04:24:01 PM

Prakash,

Some good indicators that show the VFD is in good running condition: (1) no error codes displayed on the LCD screen, (2) the VFD is operating at programmed speed, (3) no strange noises, and no visual dirt or water on the VFD, (4) the VFD is running under the maximum operating temperature - typically below 110-120°F.

You measure in AC if it is an AC inverter/VFD.

The voltage will not increase when you change the frequency/speed.

For manuals, you will need to go to the manufacturer's website. Their support/resource page will have all the documentation you need.

I am using 2 HP 3 phase ac motor to rotate a 8 kg circular shape cutter mounted on motor shaft. I want to control motor speed such that it will run at constant set speed at the time of cutting action. I used dimmerstat but speed of motor reduced during cutting action. If I use vfd, can I have constant speed as required for my application?

Jeff Condit:

08/03/2017, 04:09:54 PM

Dimmers do not tightly regulate motor speed under varying load. They merely apply less voltage. By the time you've starved it enough to slow down, it my well stall out altogether.

A VFD is different than a dimmer. They chop the signal to make it "look like" the frequency is lower. So to the extent the motor keeps running under such reduces power conditions, it will run more slowly.

Yin (Admin):

20/03/2017, 04:14:01 PM

Yes Mayur. The biggest purpose of a VFD is to maintain and control speed.

Good evening,I'm A technician by profession. Just the other day VFD for cane belt conveyor fuses exploded while in operation, what could be the problem?

Jeff Condit:

08/03/2017, 04:33:48 PM

Comment There could be any number of problems. But assuming everything remained in good working condition and this occurred there is a concept which comes into play and should be noted: Fuses open because they melt. they melt because they get hot. They get hot because they have some resistance and the current through it creates a voltage drop and hence power loss. The power lost at any instant goes like P=I^2R. So if you change a slowly moving signal like the AC line into one which toggles between off half the time and twice as big the other half, then the average would be correct, but the Power dissipated in the fuse would be nothing during the off half and 4 times as much during the on half. Hence the average overall heating in the toggled case is twice as much. Hence a fuse would blow at half the current in such a case.

Yin (Admin):

20/03/2017, 04:14:43 PM

George, how long has the VFD be operating with the conveyor?

jyoti verma:

07/07/2017, 01:49:21 AM

george fuse how much amps?? if u r using VFD i don think u have to use fuse for it

AHU motor encounter incoming phase unbalance problem.
Incoming L1,L2,L3 current 60A, 40A, 60A to VSD outgoing current was balance and VSD was not trip.
May I know whether VSD was at fault???
Please advise.
Thank you in advance

Yin (Admin):

03/02/2017, 02:06:57 PM

What is your voltage and the maximum amps of the drive? What is your VFD model?

hi,i have an iron roller press laundry machine,the vfd displays an error code cf3,and the motor stops after some time it starts, what does the error code mean, and what makes the motor to stop. I v had this problem for a long time I will really appreciate. thank you in advance

I am electrical technication I want to know that what requirement we need to set a vfD Into a motor.I am using alitvar 31 telemecanique VFD.where I get the basic troubleshooting programs

Yin (Admin):

01/02/2017, 01:15:11 PM

Hi Lino,

I am not entirely sure what requirements and troubleshooting programs you are asking for. If you are looking to size a VFD, please check out the VFD Buying Guide. If you are looking for programming instructions, here is an example video for the Mitsubishi VFD.

Ok I am a little lost on the capacitors? If they are in a DC circuit, wouldn't the electrons just collect and stay put? Or is the opening and closing of the switches on the inverter enough of a potential voltage change to release electrons?

Yin (Admin):

01/02/2017, 04:40:21 PM

Stephen,

Sorry it took us a while to respond. I have discuss this with 2 engineers, here is our answer. I hope it helps you further understand the VFD construction.

It is best to think of this as electrical energy rather than electron flow. A capacitor in an electrical circuit acts like a tank in a plumbing circuit. As current flows into the capacitor, the voltage increases. This is analogous to the level of the tank getting higher as you add more water. Thus, the capacitor stores energy just like a tank stores water. When the voltage on the dc capacitor reaches the peak voltage on the incoming ac source, then the capacitor stops charging. This is just like filling a tank with a hose. When the tank level gets high enough, the pressure in the tank will equal the pressure in the hose and no more water will flow.

The purpose of the converter (6 diodes) is to add energy to the capacitor. When the inverter (6 transistors) needs energy to send to the motor, it gets this energy from the capacitor. So all energy for the motor comes from the capacitor and the converter re-charges this capacitor as necessary to keep it close to full voltage.

IF I RUN A MOTOR AT 45 HZ WITH VFD THEN I SAVED ENERGY BUT ON THE OTHER HAND IS THE LIFE OF MY MOTOR WILL BE REDUCED AS I AM NOT RUNNING IT AT RATED CAPACITY ?

Yin (Admin):

13/01/2017, 09:05:01 AM

Haris,

No, it will not. If anything, running at 45Hz will actually extend the life of the motor because it will not be running at full speed. Theoretically, it will have less mechanical wear and less deterioration caused by heat. Hope that helps.

hello, we have VFD D700-sc for puping water with solar energy and with an automatic system.
the problem is when the tank is empty the system does not work automatically.the VFD shows a message like this E.0u3. I dont know what does that mean? please can you help us?

Yin (Admin):

12/01/2017, 02:01:11 PM

Daoui,

The error code E.0u3 refers to regenerative overvoltage trip during deceleration or stop. Here are a few possible solutions:

YOur videos and texts have been of immense help. Thank you. I have a question for you. Do these VFD's work with a single-phase induction motor. I have a single phase induction motor ( capacitor start) which I have been operated at constant speed. To meet my present applications I need to vary the speed of the motor. Is it possible to use the VFD to control the speed of the single-phase induction motor.

Thank you

Yin (Admin):

12/01/2017, 01:52:37 PM

Hi Sai,

Yes, you can use a VFD to control the speed of single phase AC electric motors. Most VFD manufacturers make single phase VFD in 230V class up to 3HP. For example, Mitsubishi has the D720S series for single phase motors. When you choose a VFD, you should make sure the VFD amps is higher than the motor amps.

What effect on vfd and motor are both different rating installed
Like vfd 40 HP and motor 25hp

Yin (Admin):

05/01/2017, 09:44:43 AM

Ashish,

Generally speaking, that is a good thing. It will work great when the VFD is bigger than the motor. The VFD will not be using its full capacity, and hence it will run slightly cooler.

You will need to check the overload rating of the VFD to see whether it is 110% or 150%. If your application requires 150% overload rating, make sure your VFD is rated for 150% also.

Second factor is if the ambient temperature of the installation is above 100°F or 37°C, you will need to make sure the VFD is bigger than the motor in terms of amps. Whether how much bigger it needs to be, it will depend on the temperature. The process of oversizing the VFD is called derating.

Assume a six-pulse VFD which is fed by a 400 V line-to-line(rms) ac line. In this VFD, the dc-bus voltage will be approximately, 540 v. It seems that this VFD can not generate 380 v line-to-line rms voltage. (the maximum line-to-line voltage will be 330v!). Is this true? in other words, six-pulse VFD can be used in 400 v grid to drive 380 v motors? in this condition, which kind of VFD should be used?
another question is that in six-pulse VFDs, over modulation for PWM-inverter is legal(in order to achieve increased voltage level in ac side?

Yin (Admin):

04/01/2017, 10:40:44 AM

Yousef,

VFDs have a voltage range. Typically 230V class has a range of 200-240V and 460V class is 380-480V. You can use these drives as long as your input voltage is within the range.

Regarding which drive to use, as I have responded to your other question, it depends on a few things, such as the motor amps, the type of machine (application), power supply, environment, etc. Without all the information, you cannot determine what VFD should be used.

I am not sure what you are asking in your last question about PWM.

Yousef:

10/01/2017, 09:38:48 PM

In the sample VFD in this page, assume that the input voltage is 400 v. Thus the dc-bus voltage will be: 1.35*400=540. It means that the maximum peak-to-peak voltage in the ac side will be 540. So the maximum peak voltage of each phase in ac side will be 270v. By this, the maximum achievable value for rsm voltage of each phase can be: 270/1.41=191v.
However, in order to generate 400v line-to-line voltage in the ac side, the rms value of ac phase voltage should be 230v,(191<230). Can you help me in this regard?

Yin (Admin):

12/01/2017, 05:31:34 PM

Yousef,

Assume input voltage is 400V. The 1.35 figure is an approximation. When the motor is off, the dc bus voltage will be (SQRT(2)) x 400 = 566V. As you load the motor, the voltage will begin to drop. When the drive is loaded, the dc bus voltage will be approximately 1.35 x 400 = 540V. The output voltage is a series of pulses. Although the peak of the voltage on the output is 540V (as opposed to 566V for a sine-wave), a 400V rms signal can still be generated by shaping the waveform. It is typical to use 400V rated drives (with 400V on the input of the drive) to provide a 380V output for 380V motors. When the output is programmed for a 380V motor, a 380V line-to-line voltage will be generated (not 330V).

The voltage on the output of a VFD cannot be higher than the voltage on the input, but it can be the same. The previous statement is not 100% true, but it is true for all larger industrial drives. Trying to use special modulation techniques to increase the motor voltage will have deleterious effects on the motor.

Hope that helps!

Yousef:

15/01/2017, 04:09:01 AM

Thanks for your response. Assuming that the input voltage of a six-pulse VFD is 400v, when the motor is loaded, the dc-link voltage will be 400*1.35=540v. If the inverter uses for example Space Vector Modulation, the maximum possible output line-to-line voltage can be:
(540/2/SQRT(2))*1.15*SQRT(3)=380v.
My question is exactly this, if we are using a six-pulse VFD which is fed by a 400v line-to-line rms voltage grid, can we provide 400v line-to-line voltage in the motor side? or the maximum possible value is 380v?

Yin (Admin):

18/01/2017, 09:27:37 AM

Yousef,

I have been talking to our VP of engineering about your question. He agrees that this is a difficult question to answer since it depends on so many factors such as power system voltage, power system voltage regulation, D.C. Line reactors, ac line reactors, drive isolation transformer, harmonic filter, motor loading, motor lead length, and etc.

For instance, if you have a 6-pulse drive with 5% line reactors, 400V power supply, and the motor is at full load, then you may not get more than 380 to the motor. But, if you put a harmonic filter on the drive, then there is a small voltage rise through the filter and you can get a higher output voltage. Fortunately, 400V power systems use 380V motors, so we seldom worry about getting sufficient output voltage.

sir,
i am having a 55KW motor used for mixer purpose(constant speed nearly 50hz)and i want to vfd to run.can i save energy by using vfd for this

Yin (Admin):

30/12/2016, 09:58:28 AM

Ravi, you could potentially save energy for a motor at that size. It depends on your run speed, run time, load, utility structure in your area. If you are running at 50Hz, which I assume is full speed for your motor, it is quite unlikely that to save any energy using a VFD. If you are running the motor at full speed, there is probably no need to use a VFD. Hope that helps.

I have one problem of VFD ..I started the motor 30 minutes after automatically stop and there shown phase unbalance fault..how can I solved this problem...

Yin (Admin):

23/12/2016, 12:00:04 PM

Hi Mukul,
You are losing a leg, so the VFD is tripping. Meaning a wire is coming loose somewhere in your system. So check your connections. It is usually the connections at the VFD. If not, check inside the junction box of the motor, or the contactor (if you have one) between the motor and the VFD. Hope that helps!

Hi sir,
What is the problem in VFD if in running time its ok but motor stopping time vfd D.C. voltage high and tripped VFD and give the message for reset.

Yin (Admin):

21/11/2016, 03:09:03 PM

Aamar,

What drive do you have?
What is the power setup? (phase, voltage, horse power of the supply power, motor, and VFD)
What is the error code?

Aamar:

26/11/2016, 10:37:48 PM

Dear sir,
I driving centrifuge that is control all data with plc showing on screen. Vfd belongs to yaskawa company.there are two motors in our centrifuge one is main drive motor 150hp.and other is back drive motor attached with gearbox 40hp.
Vfd no :400v.3phase 88A/
Vfd no:400v.3phase 208A/180A
Power 460v ,60hz.
Motor 150HP,40hp
Motor RPM1800
Panel supply output 640,639 dc volts showing on screen. But motors starting time voltage come down at 620,619 like
With control panel 150hp motor rpm 3000.

Hi, can you explain to me why overload is tripping when my 160KW motor is reaching it's rated rpm(3,600rpm). I'm using Danfoss VFD aquadrive. I already check my parameters. Thank you in advance.

Yin (Admin):

10/11/2016, 08:56:07 AM

Hi Jeff,

We will need a little more information to go on. Can you tell me the following?
(1) Your motor's FLA
(2) Your VFD's amp rating at 110% and 150% overload rating
(3) What is your application?
(4) Are there any error codes when it trips?

Feel free to respond here or give us a call at 800-800-2261, and let us know you left a comment on the blog. We look forward to hear from you. Thanks Jeff!

Jeff:

14/11/2016, 05:26:10 PM

Hi, (1) My motor's FLA is 222A
(2) The VFD's amp rating at 150% overload is 140 amps
(3) My motor is used as pump.
(4) There are no indicated error in the Control panel display of the VFD.
Thank you for your response.

Yin (Admin):

16/11/2016, 08:20:36 AM

Jeff, a team member of ours have sent you an email. Have you had a chance to send over the motor nameplate info or photo?

What is Different between VLF and VVVF and also VFD,
What is advantage and disadvantage of VFD.

Yin (Admin):

31/10/2016, 09:27:08 AM

Hi,

VVVF means Variable Voltage Variable Frequency, a term more commonly used in Asia. It is essentially the same as VFD.

VLF means Very Low Frequency. It is a particular range of radio frequency. It is not related to VFD.

VFDs are commonly used for speed control, and often a means of phase conversion (single phase to three phase). One of the disadvantages is that it distorts the current and puts out this so called, "dirty power". A line reactor will correct most of that. For more information about maintaining clean power, you can check out this video: VFD Harmonics and power quality.

Sir, Some motor manufacturers data sheet have mentioned "Type of starting: Variable voltage/frequency" and some have mentioned "Type of starting: DOL" but they also have written "VFD fed motors" What in diffence in these two motors?
Also explain is there any difference in using VFD for starting purpose and VFD for speed control,are these two related and does it affets motor selection?

Yin (Admin):

25/10/2016, 08:23:33 AM

Hi San,

Any synchronous motors can be powered by a VFD. Newer motors are generally inverter (VFD) duty, some older motors are not. However, our VP of engineer said he has used many motors that are not inverter duty with VFDs and had no problems. From what you are describing, it seems like both are inverter duty motor.

VFD can be used to start the motor as well as speed control, it will not affect your motor selection. Note that you should get a 3-phase AC motor if you intend to pair it with a VFD. I have listed a few videos below that will help you, feel free to check them out!
VFD buying guide

Should VFD frequency increased gradually until approaching the required speed to run?
or can we set the frequency immediately to the equivalent speed thatwill give and run the motor?
Any side effects?
Because I tried one time to run a VFD motor which is designed at 3600 RPM 60 Hz and I put the frequency 50 Hz to get the 2900 RPM, but the motor was suffering to accelerate to the wanted speed.

Usually I start from low frequency increasing gradually until reaching the frequency I want.

Yin (Admin):

12/10/2016, 04:27:19 PM

Hi Khalid,

Generally speaking, there are no side effects. You can set the VFD to run the motor up to 60Hz in 1 second. The VFD will get there, but the motor might take more than 1 second to get to 60Hz. It depends on the application and its load.

For your specific scenario, what is your application? What VFD do you have? What did you set the acceleration rate at? Is it getting to 50Hz or is it not going past a certain speed?

Hello if I use a motor that produces 237kW and 17000Nm torque at 127rpm and use a VFD to bump down the RPM to about 3 which is my requirement, will the torque be amplified respectively?

Yin (Admin):

18/10/2016, 10:42:20 AM

Hi Sahil,

The torque will remain constant. However, your motor will likely overheat if you run it at 3 RPM because the motor fan is not spinning fast enough to cool down the motor. We generally suggest not to run the motor lower than 20% of its rated speed because of that reason. I hope this helps!

Your comment is 100 % correct but our problem is drive running up to 10.5 Amps(5.5kw) more than 10.5 Amps its immediately tripping ACS550-01-12A-04 we have to go how much drive capable FLA setting with safe running condition. can i know your contact no.

Yin (Admin):

27/09/2016, 08:16:53 AM

Hi Nagula,

Did you by chance see the response I sent to your email yesterday? I don't quite understand your question. You are welcome to call us at 800-800-2261.

we are having acs550-01-12a-04 for application is fine coal discharge serew conveyor 5.5kw problem is immediately tripping with overload alarm limited seting is 12.5a replacing vfd to motor and arrange to dol starter running with 10-12.5a why it is not running with vfd.

Yin (Admin):

22/09/2016, 03:16:26 PM

Nagulmeera,
If your VFD does not ramp up at all but trips immediately; you should check your FLA (amps) parameter. You need to set the FLA to match your motor's FLA. If that is correct, check all of your wiring of the VFD. If that is also correct, I would pull the leads and check your motor with a meter. You are having some sort of ground fault or line to line short circuit. Hope that helps!

Can two motors be controlled by one VFD controller. Have have both running a the same time??
We have this situation at our water plant. THE VFD of course run warm to hot?

Yin (Admin):

21/09/2016, 10:48:22 AM

Chip,

Yes, you can with a couple of conditions. You will need a VFD with an FLA (amps) higher than the two motors combined, plus possible derating based on altitude and ambient temperature. The limitation is that you have to start and stop the two motors at the same time with the same setting. If you need help choosing one for your pumps, feel free to contact us at bdt@emcsolutions.com or call us at 800-800-2261.

appreciate your attention
so if I want to control frequency in an induction heating system (without motor) what can I use

Yin (Admin):

21/09/2016, 11:15:08 AM

Ali, we have no expertise in induction heating system, so we cannot make any recommendations. I would suggest contacting the manufacturer of your system to see what they advice. Sorry we cannot be more helpful.

What is the problem if the fuses before the transformer gets busted? it always happen in the Plant on the VFD's for Cooling Tower fans. your advise would be highly appreciated.

Yin (Admin):

31/10/2016, 10:59:09 AM

Roly,

Are the fuses blowing every time you start the motor? Then you need to have an electrician check all of your wiring. It could be a thousand different things, control wire, power wire, power to neutral, short to ground, cross phase, etc. You need to turn off the power and check everything. Use the method of elimination to narrow down the possibilities. Make sure you follow any safety protocols when you inspect your equipment.

If the fuses are blowing randomly, then you should start by checking your current and see what you are getting.

Hello - would a VFD be useful when the power supply is single phase 240V 50Hz ... but the motor is a 110V 60Hz one ?

VFDs.com Admin:

08/09/2016, 06:59:18 AM

Hello John,

VFDs output three phase power, therefore, cannot be used on single-phase motors. A VFD rated for 240V input can accept an input voltage of 200-240V at a one frequency, single- or three-phase power, and output the same or different voltage at a different frequency. For example, if you had single-phase, 200V @ 50Hz power, you could use a VFD to supply power to a three-phase, 240V @ 60 HZ motor.

I have a question what will be the voltage at motor terminals when RPM of motor is zero?
Motor is 37 KW and is connected with VFD made by ABB.

Yin (Admin):

07/09/2016, 08:55:48 AM

Asim,

When the motor is not running, you should have minimal voltage readings (close to nothing) at the terminals. Be careful when you check the readings, you should always wear proper protective clothing and equipment. Hope that helps.

Comment
Am pleased with this technological innovations. The explanation about VFD system triggers every industrialist to run, purchase and install. In reality, the benefits are tangible. Even a lay man can understand this. Infinity Thks. Ibra - Production Supervisor.

What is expected life of VFD?
Is its costs worth over its useful life?

Yin (Admin):

20/07/2016, 04:39:41 PM

Hello Alind,

What is the expected life of a VFD?
If a VFD chassis is simply mounted on the wall, with no protection from dust and particulates, many manufacturers are prediction a lifespan of 5-7 years. The secret to VFD longevity is to keep it cool, clean, and free from dust, particulates, and other environmental hazards. In most instances, this is done by putting the VFD in a positive pressure ventilated cabinet with air filters. The air filters should be accessible from the outside of the cabinet and easily changeable. The filters should also be readily visible. Otherwise, the maintenance staff tends not to change them as they get dirty. We have many VFDs in cabinets of this type that have been in operation 25 years and longer.

Is a VFD worth the cost?
In most applications, a VFD will pay for itself within 1 to 3 years. Of course, this is only a general rule of thumb. In some cases VFDs can pay for themselves in only a few months. In other cases there is little or no savings. But, in the wide majority of applications, there is a significant energy savings.

sir is there any vfd inverter stablizer for air conditions which i can save money on electicity and run my ac slilent with out tourq and

Yin (Admin):

18/07/2016, 10:47:56 AM

Amer,

I am not quite sure what you mean by VFD stabilizer.

You cannot use a VFD on household air condition units. If you are using it with an industrial chiller, VFDs will allow you to control the speed of the motor which may in turn save electricity consumption, but it will not make your chiller run any quieter.

Great article - I understand how a VFD works. I'm looking for more info on control of the VFD vs control valves. I have a central plant (hot water) feeding multiple air handlers, each has its own valve for the heating coils, current circulating pumps run full-bore with a by-pass loop for when control valves are closed. Boilers run as required to maintain loop temperature. If I upgrade to VFD pumps, can I drive the speed of the VFD (say 1-100% speed) based on the valve positions (say 10 @ 20% to 10 @ 80% open, or some combination) through my BAS system? The BAS system drives the actuating valves - I'd want to summarize their positions to create total current system demand, and drive the pump at that speed, and more or less eliminate the need for the by-pass loop. Any good articles on how to control the VFD?

Here's the key question - any good studies / white papers on the economics of this? The powers that be want to know... Technology is great and all, but without something simple to understand to put in front of decision makers, it's hard to 'sell' it without getting into the technical lingo. Nothing sucks more than trying to explain technical stuff to a non-technical crowd - *blank stare*, but talk $$$ and we can implement energy savings measures.

Yin (Admin):

13/04/2016, 09:14:06 AM

Hi Steve!

I have chatted with our VP of engineering Craig, who is in the video, and unfortunately he has not done any white papers about energy savings. He said he had been involved in two energy saving projects (one of which we wrote about, is the Industry Spotlight: Using VFDs with Reciprocating Compressors article posted on March 20, 2015) and he had done the calculations for each of the project, but he did not create any white papers since that was not his goal.

We understand all too well how difficult it is to explain the benefits of an equipment and trying to convince someone to spend a large sum of money for it. However, based on our experience we are not completely convinced that having white papers will change the minds of our customers more than having professionals like Craig here to talk to them. So as much as we would love to provide you with some more materials on energy savings, we cannot help you with it at the moment. On another note, we have created an energy saving video, have you seen it? Saving Energys Using Variable Frequency Drives

Steve:

13/04/2016, 09:30:44 AM

Thanks for the response Folks!

Great quick little summary, the chart showing operating curves of damper/valve control vs VFD is a great visual to illustrate the savings. I especially liked the 107% pressure requirement for flow restricted conditions. Discussion around a <1yr pay-back on the investment really sells the case.

When you design the system, the pumps/fans have to be sized for 100% load, however in reality 100% is rarely called for. Variable speed (VFD or otherwise) simply makes sense - why run the motor at 100% all the time? Especially for HVAC, when the operating point is typically 25%-50% of total demand load for most of the season.

Interesting that this technology has been around for a couple of decades, but not widely adopted. I've heard a lot of chatter about signal interference / stray frequencies generated by VFDs, which causes all kinds of nightmares (blown motor windings, control system interference, etc.) - especially for retrofit to existing pumps/fans. Do you recommend replacing motors or just installing the VFD control module in this case? I trust the technology has come along far enough to control these hiccups. Is there design guide, or do you offer design support to engineers looking to apply this technology (like me)?

Yin (Admin):

13/04/2016, 10:10:39 AM

Steve,

You are right about HVAC. HVAC and pumps are among the most common applications for VFD. Many modern VFDs also have a set point control function called PID (Proportional–Integral–Derivative) and it is very important to many HVAC and pump users.

We like to think that VFDs are pretty common these days, you will unlikely notice them outside because they are always in electrical boxes, or they are hidden in a basement corner of a building. But we also know there are many opportunities out there to expand this technology. Unfortunately VFD is not a cookie cutter type of equipment, if you will, and people may not be willing to invest the time to learn about it even though it provides a great deal of benefits in their operations.

Regarding to signal interference and stray frequencies, you might be referring to what we call harmonics. Here is a video of Craig explaining the gist of harmonic distortions . VFD Harmonics and Power Quality VFDs do produce harmonics and could potentially cause a problem to power quality. It is a real thing, so much so that we actually have a power quality expert in our company. The bigger the VFD, the more you need to pay attention to it. We think the most cost effective way to eliminate harmonics is using line reactors or harmonic filters. These additional equipment may also be part of the reason that turns people away from this technology. Here is a more lengthy article about harmonics written by Craig: Harmonics Mitigation .

Now about retrofitting existing motors, or any motors in general, we would always recommend pairing with a VFD if you need speed control. What kind of design support are you looking for specifically? Our company specializes in automation integration, from generators to motors to VFDs. I am sure we can help you with what you need. If you would like, you are always welcome to get in touch with us about your project. You can email us at bdt@emcsolutions.com, or call us at 800-800-2261, or continue to chat with us here!

mark:

25/04/2016, 01:21:36 AM

Steve forget the guessing using valve position. Use a differential pressure transmitter across mains, usually at a higher location in building as input to bas and let bas control speed. Transmitter could also be wired to vfd for feedback as most decent drives have built in pid controllers. bas is better so you can motor or log pressure.

Good information I get, but I needs more information regarding that I already fwd some messages, buy overall very good information ur giving through this media. So thanks to u n ur full team. Krishna pednekar from India presently n Egypt.

dear sir please guide me . for one application I am using 3 phase 450 V 50 hz RPM 1000 motor. I want to use VFD controls for to obtain 250 rpm 500rpm . can we use vfd controls for 3phase ac motor. who is making & what is the cost?is there any limitations . lese inform
Best regards
D.R.Kulkarni
9960021517

good morning. I have confusion in VFD rated motors. We are running our equipment with constant speed. We are exporting our equipment to different countries. Since power supply in different countries are different, each time we have to purchase the motor according to the country specified power supply. to overcome this issue, we are purchasing VFD rated motor. Will the VFD rated motor works in different countries?. To elaborate this, I am putting below example.

I am rotating a cooling drum with constant speed of 10rpm. I have used a VFD rated geared motor with 0.75kw & connected to power supply of 3ph,415v, 50Hz. Now can I use the same motor with power supply of 400v, 60Hz. there will not be any change in o/p speed (10rpm). Could you please reply.

i am a bit lost on VFD/rotary phase converters. would they supply constant on demand power while it is on? i've got a sewing machine with a servo motor. its MAYBE 1/4hp (the motor itself is about the size of a 12oz soda can around, slightly shorter height)

the only thing i am not sure about is if VFDs would be okay for low load frequent start/stops

this machine also has electronics/small LCD display. would a VFD be okay to use with the electronics? i really want to avoid using a rotary converter if i can because of the size/noise

Please share that what will happen to the motor power and torque after the installation of VFD when it is operated at the lower frequency and rpm then its designed one. Will the torque reduce after reducing the rpm?

Please share that what will happen to the motor power and torque after the installation of VFD when it is operated at the lower frequency and rpm then its designed one. Will the torque reduce after reducing the rpm?

Please share that what will happen to the motor power and torque after the installation of VFD when it is operated at the lower frequency and rpm then its designed one. Will the torque reduce after reducing the rpm?

If you have a three phase motor and single phase power, yes. You can find single phase input VFDs from many manufactures. Typically they go up to 3HP. Anything above 3HP, you will have to derate the drive by getting a VFD that is twice the size (in Amps) of your motor.

If you go the route of derating the VFD, it is important to know that the VFD has to go directly to the motor and nothing else should be powered downstream by the VFD. Any lights or switches should be powered from a separate source.

Hope that makes sense. If you have other questions, feel free to send us an e-mail. Thanks.

I've noticed some inverters can be fed with single phase but output three phase. Is this true of al inverters. How does it produce the phase shift required for the third leg. Are the three legs 120 degrees apart. Unlike single phase.

admin:

28/09/2015, 04:02:35 PM

Hi Joe,

All AC Variable Frequency Drives are designed to control 3-phase motors, but not all of them will accept single phase power input. The output of the drive is not exactly a true 3-phase AC power, it is a DC generated square-wave, simulated 3-phase power.

All of the input power is inverted through diodes to create DC power so the drive is able to monitor and control the power, then the DC power is ran through IGBTs that “pulse” the DC + and – currents to create the simulated 3-phase power.

The output legs are 120 degrees apart.

AC drives are specifically designed to control 3-phase AC motors, they are not designed for any other function. For more information about how a VFD works, here is a video of our VP of engineering explaining what a VFD is: https://www.youtube.com/watch?v=wDZANW2HeJ8

Many many thanks for this very useful information.
Your Diagrams and simple explanations has made this complicated topic very easy.
I feel like I understand all about VFDs now only :)
and I am excited to read and reply to all your blogs .

That was good information regarding VFD, VFD itself the answer of speed control.My question is if my Process Reactor's RPM is set with 68 max.so is it possible with the help of VFD i can make my RPM more than 68? if no that mean VFD means always decrease the RPM not increase...am i right?

Dear admin, actually in my area only 3hours will be 3 phase current available, the remaining timetime will be 2phase current only, in this situation can i use VFD for my submersible water pumb on 2phase current?

Azeez Monsur:

14/07/2015, 11:22:35 AM

I doubt if this can work, as some VFDs experience undervoltage when required phase is not complete. You need a complete 3-phase input to avoid the devise from being tripping off.

I'm running 5.5 kw motor coupled to 7.5kw inverter. The motor draws 10.7 amp when 400v and 50hz when running with inverter its frequency will drop to 28hz and how much the vo lol tage and current would be at this time will burn my motor.

admin:

13/07/2015, 10:11:00 AM

Iahiru,

We need a little bit more information. Did you set the parameter for speed to 50 Hz maximum? Does it ramp up to 28 Hz and stop?

I really over spec'd a ventilation fan/motor. 30 HP 460V. Should have been 20 HP. Does the VFD have to be rated for the existing motor or the speed/draw I want to operate at?
My guess is the VFD has to be 30 HP.

Thanks

admin:

13/07/2015, 09:06:00 AM

Tim, you are correct. You have to size the VFD based on the motor's spec. More specifically, you have to find a VFD that has a higher or equal amp rating than the motor.

How much can we load a VFD for ESP's (electro submersible pumps) applications? Its true if we under load a VFD do we have more chance to get harmonics than if we load it properly ( let's say 80-90% )

admin:

11/03/2015, 02:47:00 PM

Hello Roberto,

Sorry for the delayed response. We consulted our field engineer about your questions. The lighter you load a VFD, the higher the harmonic distortion will be. If you stay within about 15% of the full current of the VFD, it should be fine.

We are unsure what you mean exactly when you "load the VFD". If you are asking how close can you get for sizing, then it is typically within 5%; possibly closer if the pump is only moving water. Technically, you can use the full range up to the rated current rating. However, we generally like to be conservative and not be right at the top of the range of the VFD rating.

If you are asking about overload conditions, the drive will run to the preset overload values that are in the drive as it relates to the parameter set points (i.e. 110% for 60 seconds at SLD rating of hte FLA in parameter #9 [Mitsubishi], or 150% for 60 seconds at LD rating of the FLA)

can v use single phase phase motor with single phase vfd? in other words i m going to make my course project i m going to make a prototype of my idea and in this idea i m going to design a vfd motor and initially i m going to use very low power motor with vfd

Yaseen Subahani:

05/03/2015, 09:49:07 PM

Yes u can use single phase motor with single phase vfd. And I already done this project.

admin:

11/03/2015, 02:50:00 PM

Theoretically, yes you should use a single phase vfd for your single phase motor. However, single phase VFDs are not very common. We haven't heard of that many in the market.

How does the VFD work in varying the frequency and voltage supplied to the electric motor.

admin:

21/01/2015, 10:45:00 AM

Bakare,

The VFD is able to vary the frequency and voltage through the use of IGBTs. It is through the fast switching of IGBTs, which creates PWM wave, that allows the VFD to alter the frequency and voltage supplied to the motor. You can read more about IGBTs in another post on our blog here at:http://www.vfds.com/blog/switching-it-up-igbt.

How should we choose an appropriate VFD ? Let's say we have a X KW motor, what kind of VFD shall we consider ? I mean, the maximum and minimum limits in KW.

admin:

29/12/2014, 07:42:00 AM

Silviu,

When sizing a VFD to a motor you want to match the FLA listed on the motor nameplate to the amp rating on the VFD. You will need to consider what application you have because this will determine what overload rating you will need on the VFD. Take a look at our VFD buying guide here:

http://www.vfds.com/blog/vfd-buying-guide

This article will help you better understand everything that needs to be considered when sizing a VFD.

This is really informative material which you shared with us. Thank you very much... Can you help me out with this, I were working on micromaster 440, it gives fault indicates overcurrent error. I unplugged the motor termination, on the drive but still found the same error. I know the drive is faulty but I am interesting to know what were the reason.. Is it the transistor malfunction or capacitor or any other? I will be very thankful if you upload some troubleshooting case studies related with VFD repairing.

Thanks
Service engineer

Muneeb:

22/12/2014, 12:45:35 AM

I would be very thankful if you clarify me in below contents
I found at motor input from drive, we occasionally placed chock transformer. I heard the purpose of it is motor protection, but how it protects if AC square wave is appropriate for motor operation as you told in article..

Thanks in advance

admin:

22/12/2014, 12:38:00 PM

It is really hard to say the exact reason for your overcurrent error without being able to directly take a look at the drive. There could be several reasons why you are having problems. Our recommendation would be to take it somewhere for diagnostics. If your location is close enough to us, you could send the drive in to us fpr diagnostics to address the issue. If you would like to do that, we can send you a repair quote.

As for your other question about DC chokes. A choke reactor is usually used on a dc bus of a drive to help with harmonics that goes back on the line.A Dv/dt filter or sine filter will help with the square wave form, which you mentioned. If the motor is not too far away from the drive it isn’t too much of a concern if you don't have one, but if it is 100 ft from the drive you should take a look at using one.

Why would the switchgear that is feeding the VFD show a different current reading to that showing on the VFD?

admin:

17/12/2014, 08:43:00 AM

Without knowing more about your application it is hard to give a definitive answer. But, typically they will be different because the VFD and switchgear are not calibrated the same. The amperage that you will see from your switchgear will include everything that is on the switchgear while the amperage from the VFD is just from the motor.

Bryan Charlton:

17/12/2014, 08:49:06 AM

Sorry that was a bit misleading by me the current reading on the MV switchgear is of the CB feeding the VFD so it is dedicated to this application only.

Bryan Charlton:

17/12/2014, 09:08:16 AM

I should add also that the VFD is reading less than the switchgear up until the rated frequency which then they are identical.

There are several reasons that might cause a DC over voltage. It is hard to identify the reason for this with out knowing more about the application. If you would like to call in and talk with one of our engineers at 800-800-2261 we can help you figure out what is causing your over voltage.

what would be the minimum DC voltage from DC voltage source on DC bus of VFD to run the induction motor?

admin:

03/12/2014, 09:27:00 AM

The DC bus voltage is directly related to the supply voltage. There is a DC bus voltage at which the VFD will trip on under-voltage and will not run at all. This will vary depending on the drive manufacturer. For one brand of drive that we offer, the DC bus under-voltage trip is set at 430V for a 480V drive. The typical DC bus voltage for a 480V drive is about 650V. Technically speaking, there is no absolute minimum voltage that the DC bus will function at, but rather a minimum source voltage that the VFD will consider acceptable voltage to operate safely.

Yes, it does. Base on the overload rating of the VFD, it can give you full load torque and more at all speeds, including dead stop without the typical high current associated with across the line motor start.

I have seen VFDs offered with 120V single phase input and 230V output. How can you get 230V out of 120V without a transformer?

Jon Novak:

22/10/2014, 11:55:35 PM

240V output is no more than 2x 120V lines phased @ 180degrees. Likewise 208V 3phase is 3x 120V lines phased at 0, 120, and 240 degrees. If you are handy with how you capture the AC power and convert it to DC, you can get a + and - DC rail at the cost of needing more current. Which will allow you to use the VFD portion to phase the output and get you the phasing you need to get "2 phase" 240, or 3 phase 208.

FYI in your house, this is exactly how its done. You generally get a neutral and 2 hot legs legs of power each having 120V (to neutral). But hooking Hot/Hot will give you 240, since they will be 180 out of phase.

Jun Pascasio:

29/01/2015, 10:38:41 PM

A device called Joule thief can do that. It is a configuration of a capacitor and an inductor. The configuration causes a build-up of charge at the output terminals. The oscillations on the R-C circuit makes it possible.

The above equation shows us that there is a third element outside of speed and power that must be taken into account. Torque is determined by the load. Essentially while there are small losses in power in the VFD and the motor (both are extremely efficient) you will not be able to determine the consumption of power without knowing the torque.

What controls are out there to determine the output frequency in order to match the load? In an heat pump application is this controlled by temp sensors and programmed logic similar to a traditional technology?

Is it possible to use 2-wire hard contact to remotely vary the speed of the motor between 50% and full speed when using your VSD device.

Thanks

Engineer Samson rotimi Oladipo

admin:

12/08/2014, 06:17:00 PM

Yes, the drives include preset speed inputs. The two wire contact would be wired to the preset digital inputs.

SAMSON OLADIPO:

01/09/2014, 04:51:13 PM

Thanks for the answer, the actual thing we want to achieve is, if the two-wire hard contact are bridged we want to have 100% full speed and if the wires are disconnected, the motor should be running at 50% speed. Is it possible ? and how can we achieve this with the preset digital inputs. Could you help us with a typical sketch or diagram or drawings.

In the V/Hz discussion I can't find the reference "(see the VFD Motor Theory presentation for more on this)" . Where is it located?

This site is a great, informative discussion of VFDs.

admin:

01/07/2014, 04:56:00 PM

Thanks for the kind words and for your question! We are currently in the process of editing the motor theory post but I think I can help answer your question about the V/Hz ratio.

Motors are driven by magnetic poles. The strength of the magnet is proportional to the ratio of the voltage divided by the frequency (V/Hz). If the ratio is too low, the motor will be too weak to provide full torque on the motor shaft. On the other hand, if the ratio is too high, the iron in the motor will saturate because it is being pushed too hard. It will overheat and start to smoke, and eventually fail. Therefore the ratio must remain constant.

To illustrate this further, at 460V and 60Hz, the magnetic flux ratio (V/Hz) is 460V/60Hz = 7.66 V/Hz.

Now it’s important to remember that this V/Hz ratio must be maintained in the VFD. When you reduce the frequency you must also reduce the voltage. If you were to reduce the frequency, say to 30Hz, the new required voltage to maintain the ratio would be approximately 230V.